The IceCube project has transformed a cubic kilometer of natural
Antarctic ice into a neutrino detector. The instrument detects more
than 100,000 neutrinos per year in the GeV to PeV energy range. Among
those, we have isolated a flux of high-energy neutrinos of cosmic
origin, with an energy density similar to that of high-energy photons
and cosmic rays in the extreme universe. We recently identified their
first source: on September 22, 2017, several astronomical telescopes
pinpointed a flaring galaxy, powered by an active supermassive black
hole, as the source of a cosmic neutrino with an energy of 290
TeV. Archival IceCube data subsequently revealed in 2014 a flare of
more than a dozen neutrinos from the same direction. At a distance of
four billion light-years, ten times further than the nearest such
sources, the first cosmic ray accelerator seems to belong to a
special class of active galaxies that may be responsible for the
origin of the highest energy particles in the Universe.